The proposed research can be divided into five different types of studies: (1) At least three studies of behavioral treatment of obesity: one will investigate the effects of spousal support with and without medication on weight loss and maintenance of weight loss. One will investigate the effects of treatment at the work site as compared with medical auspices. One will ascertain the effect of different schedules of reinforcement on weight loss in a commercial weight reduction program. (2) Three forms of non-behavioral treatment: jejunoileal surgery, gastric bypass surgery and psychoanalysis. (3) Genetic studies of obesity will consist of three twin studies: using the NRC/NAS twin register, the Kallman register of twins selected for the study of aging and Shields data on monozygotic twins brought up together and brought up apart. Adoption studies will be carried out by use of the Danish Adoption Register. (4) Intensive non-participant observation of families containing an obese and a nonobese daughter within two years of each other in age. (5) Other studies with an emphasis on both caloric intake and caloric expenditure (physical activity).